The overall objective of this proposal is to study the structure and function of cytoplasmic filaments in cultured endothelial cells derived from the throacic aorta and portal vein. A multidisciplinary approach using cell culture, phase microscopy, polarization microscopy, immunofluorescence microscopy, Nomarski differential interference contrast microscopy, electron microscopy, immunoelectron microscopy, and biochemistry will be used to study the structure and function of the intermediate filaments ("100 A filaments", approximately 10 nm in diameter) and the actin filaments ("microfilaments", approximately 6 nm in diameter) in endothelial cells. This research project is based on the hypotheses that: (A) the intermediate filaments may participate in transport and localization of organelles (e.g., lysosomes and mitochondria) and macromolecules (e.g., lipoprotein), within the cell, and (B) the actin filaments may function (1) as a cytoskeleton -- maintaining cell shape and attachment to the substratum and (2) that they may also operate in endothelial cell contractility.